A CUTTING INSERT WITH A VARYING CHAMFER ANGLE AT THE NOSE CUTTING EDGE

Description

Background of the invention

[0001] The present invention relates to a metal cutting insert that is primarily intended for turning operations.

[0002] For all sorts of turning operations, there is a certain interplay between the feed rate and the corner radius, the corner radius being the connection between the main cutting edge and the secondary cutting edge. The surface fineness produced on the workpiece is specifically influenced by the interplay between the corner radius and the feed rate. The approach angle is defined as the angle between the main cutting edge and the direction of feed. This angle has a considerable influence on the interrelation between the different cutting force components, and thereby also on the surface fineness and dimension accuracy. Surface fineness and dimension accuracy are very sensitive to changes of the approach angle. One problem for all turning operations is to obtain the desired surface fineness. Another problem is poor tool life.

[0003] Embodiments of prior cutting inserts are shown in EP 1226892 A2, which discloses a cutting insert according to the preamble of claim 1, and DE 10308234 A1.

Objects of the invention

[0004] One object of the present invention is to provide a cutting insert that improves the fineness of the machined surface.

[0005] Another object of the present invention is to provide a cutting insert that significantly improves tool life.

[0006] Still another object of the present invention is to provide a cutting insert that improves surface finish over the total tool life.

[0007] Still another object of the present invention is to provide a cutting insert that reduces influence on residual stresses in the work piece surface.

[0008] Still another object of the present invention is to provide a cutting insert that reduces influence on hardness in the workpiece surface.

[0009] Still another object of the present invention is to provide a cutting insert that reduces the sensitivity of a turning cutting insert relative to the positioned approach angle.

[0010] Still another object of the present invention is to provide a cutting insert that reduces the radial forces during turning.

[0011] Still another object of the present invention is to provide a cutting insert that reduces provides for a smaller variation in cutting edge position when used in a tool holder.

[0012] These and further objects have been attained by a cutting insert as defined in the charactering portion of appended independent claim.

Brief description of the drawings

[0013] The objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawing in which like numerals designate like elements, and in which:

FIG. 1 shows a plan view of a turning cutting insert according to the invention.

FIG. 2 shows the cutting insert in a perspective view.

FIG. 3A shows a cross-section according to the line E in Fig. 1.

FIG. 3B shows a cross-section according to the line F in Fig. 1.

FIG. 3C shows a cross-section according to the line G in Fig. 1.

FIG. 3D shows a cross-section according to the line H in Fig. 1.

FIG. 3E shows a cross-section according to the line J in Fig. 1.

FIG. 4 shows a plan view of a corner portion of the cutting insert in magnification and in plan view.

FIG. 5 shows the corner portion in a side view.

FIG. 6A shows a graph of chamfer angle range at the different cross-sections according to lines E-J in Fig. 1.

FIG. 6B shows a graph of chamfer height at the different cross-sections according to lines E-J in Fig. 1.

FIG. 7A shows the cutting insert during turning of a work piece and Fig. 7B shows portions of the cutting insert and the workpiece.

Detailed description of preferred embodiments of the invention

[0014] In the figures 1 to 5 a turning cutting insert 10 according to the present invention is shown. The cutting insert may be either single- or double-sided. The cutting insert is rhombic, the corner portion shown in FIG. 1 having a nose angle of about 60 to 80°. However, it may also be square, rectangular, triangular or hexagonal. When it is hexagonal, it may also be in the form of a so-called trigonal insert. The insert in this embodiment is made of cemented carbide having a cubic boron nitride (CBN) corner portion, but may also be made completely of any of those materials or of any other suitable material. The cutting insert 10 comprises an upper surface 11, a lower surface 12 substantially parallel with said upper surface, and at least three side surface 13A,13B extending between said upper and lower surfaces. The upper surface 11 is planar in this embodiment and extends perpendicularly relative to said at least three side surfaces. A transition between two adjacent side surfaces 13A,13B forms a rounded nose radius surface 14A at a cutting insert corner 14.

[0015] The cutting insert 10 comprises a peripheral land 15, constituted by at - least two peripheral lands 15A and 15B, bridging the upper and side surfaces at least at the corner portion 14. The peripheral lands 15A and 15B in this embodiment encircles the entire cutting insert periphery. The peripheral lands 15A and 15B in this embodiment are of different configuration. The peripheral lands 15A and 15B slope at chamfer angles β_A-β_E (as illustrated by Figs. 3A-3E) relative to a plane P containing the upper surface 11. The peripheral land is adapted to strengthen the cutting edges of the cutting insert. In this embodiment the upper surface 11 is planar and connects directly to the peripheral land 15 to allow a strong configuration. An intersection of the peripheral land 15 and the nose radius surface 14A forms a nose cutting edge 16. The nose cutting edge 16 is defined by at least one radius R1. Each operative cutting corner 14 comprises at least one convex wiper edge 17, 18 connected to the nose cutting edge 16. In this embodiment there is provided a first 17 and a second 18 wiper edge separated by the nose cutting edge 16. The nose radius surface 14A may be symmetrical with respect to the corner bisector B. This results in the advantage that the cutting insert becomes symmetrical, thereby enabling both left-hand and right-hand turning with the same insert, i.e., both left-hand and right-hand holders may be used for this cutting insert. The cutting insert 10 in this embodiment has a through-going hole 21 extending perpendicularly to the surfaces 11 and 12.

[0016] Referring especially to Figs. 3C and for example 3E, the chamfer angle β_c in a cross-section at the nose cutting edge 16 is larger than the chamfer angle β_E in a cross-section a distance away from the nose cutting edge 16. The chamfer angle β_C in the cross-section at the nose cutting edge 16 is larger than the chamfer angle in a cross-section at said first 17 or second 18 wiper edge. The peripheral land 15A and 15B follows a substantially straight line in a cross-section through the cutting insert 10, such as shown in Figs. 3A-3E. The peripheral land 15 has a continuously varying chamfer angle β at the corner portion 14. The chamfer angle β_C, in a cross-section as illustrated by Fig. 3C at the nose cutting edge 16, is larger than the chamfer angle β_E in a cross-section at the first wiper edge 17. The peripheral land 15 in a plan view has a substantially constant width W_A W_E, as illustrated by Figs. 3A-3E. The land width W_E is however slightly larger than the widths W_A-W_D. Alternatively, the land widths may vary similar to the variations of the chamfer angle.

[0017] The first wiper edge 17 is defined by at least one first wiper radius R2 and the second wiper edge 18 is defined by at least one second wiper radius R3, said radii R1-R3 have different points of origin. The radii R2 and R3 can be equally large. The peripheral land 15 at each first and second wiper edge 17, 18 has a continuously varying chamfer angle β. Referring to Figs. 3A-3E and Fig. 6A and 6B, the angle β_A is chosen within the range 5 to 20°; the angle β_B is chosen within the range 10 to 30°; the angle β_C is chosen within the range 15 to 60°; the angle β_D is chosen within the range 10 to 30°, and the angle β_E is chosen within the range 5 to 20°. Furthermore, the projected height Z of the chamfer when viewed perpendicular to the side surface 13A, 13B or nose radius surface 14A may vary in the range disclosed in Fig. 6B or as follows (in mm):

A	B	C	D	E
0.004	0.009	0.01	0.009	0.004
0.18	0.29	0.86	0.29	0.18

[0018] Referring now to Figs. 7A and 7B that show the cutting insert during turning of a work piece 19 and an enlarged portion of the cutting insert and the workpiece during a hard turning process, respectively. Usually the depth of cut Y is equal to or less than the nose cutting edge radius R1, such that the uncut material for example does not reach the bisector B. The insert is positioned with a clearance angle σ beyond the wiper edge 17. The size of the chip 20 to be removed is determined by the depth of cut Y and the feed per revolution X. The thickness of the chip transfers into zero at the convex wiper edge 17. Since the peripheral land 15 has a chamfer that is most blunt at the bisector of the corner portion 14 that portion withstands wear while the wiper edge 17 that cuts the thin part of the chip is relatively sharp a good surface fineness is obtained. The fact that that the peripheral land 15, 15A,1 5B in a plan view has a substantially constant width W_A-W_E provides for a smaller variation in cutting edge position when used in a tool holder.

[0019] In the described embodiment the active corner of the cutting insert is a section of CBN and thus the cutting edges 16, 17 and 18 are comprised of CBN. Alternatively any other suitable cutting material can be used all due the machining application.

[0020] When using cutting inserts having wiper edges the radial forces become high compared to conventional cutting inserts without wiper edges. A cutting insert according to the present invention has a more blunt chamfer angle about the bisector of its cutting corner to protect the corner from breakage during high feeds while the wiper edge has a less blunt to diminish the radial forces. Thus, a cutting insert for turning is proposed that improves the fineness of the machined surface and significantly improves tool life.

Claims

1. A cutting insert for turning comprising an upper surface (11), a lower surface (12) substantially parallel with said upper surface, and at least three side surfaces (13A,13B) extending between said upper and lower surfaces, a transition between two adjacent side surfaces (13A,13B) forming a rounded nose radius surface (14A) at a cutting insert corner (14), said cutting insert comprising a peripheral land (15,15A,15B) bridging the upper and side surfaces at least at the corner portion (14) at a chamfer angle (β_A-β_E), and an intersection of said land (15,15A,15B) and said nose radius surface (14A) forming a nose cutting edge (16), said nose cutting edge (16) being defined by at least one radius (R1), said cutting corner comprising at least one curved wiper edge (17,18), Whereby
the chamfer angle (βc) in a cross-section at the nose cutting edge (16) is larger than the chamfer angle in a cross-section a distance away from the nose cutting edge (16) and characterized in that the peripheral land (15,15A,15B) in a plan view has a substantially constant width (W_A-W_E).

2. The cutting insert according to claim 1, characterized in that the chamfer angle (β_c) in the cross-section at the nose cutting edge (16) is larger than the chamfer angle in a cross-section at said wiper edge.

3. The cutting insert according to claim 1 or 2, characterized in that the peripheral land is provided as a chamfer (15) encircling the entire cutting insert periphery.

4. The cutting insert according to anyone of the preceding claims, chara cterized in that the peripheral land (15,15A,15B) follows a substantially straight line in a cross-section through the cutting insert.

5. The cutting insert according to anyone of the preceding claims, chara cterized in that the peripheral land (15,15A,15B) has a continuously varying chamfer angle (β) at the corner portion (14).

6. The cutting insert according to claim 5, characterized in that the chamfer angle (β_C) in a cross-section at the nose cutting edge (16) is larger than the chamfer angle (β_E) in a cross-section at a first wiper edge (17,18).

7. The cutting insert according to anyone of the preceding claims, chara cterized in that the cutting corner (14) comprises a first wiper edge being defined by at least one radius (R2) and a second wiper edge being defined by at least one radius (R3), said radii (R1-R3) have different points of origin.

8. The cutting insert according to claim 7, characterized in that each first and second wiper edge (17,18) has a continuously varying chamfer angle (β).

9. The cutting insert according to anyone of the preceding claims, characterized in that the cutting insert (10) partly or completely is comprised of cubic boron nitride.

Ansprüche

1. Schneideinsatz für das Drehen mit einer oberen Fläche (11), einer unteren Fläche (12), die im wesentlichen parallel zu der oberen Fläche ist, und wenigstens drei Seitenflächen (13A, 13B), die sich zwischen den oberen und unteren Flächen erstrecken, wobei ein Übergang zwischen zwei zueinander benachbarten Seitenflächen (13A, 13B) eine abgerundete Nasenradiusfläche (14A) an einer Ecke (14) des Schneideinsatzes bildet, der Schneideinsatz eine periphere Fase (15, 15A, 15B) aufweist, welche die obere Fläche und die Seitenflächen zumindest an dem Eckenabschnitt (14) unter einem Fasenwinkel (β_A-β_E) überbrückt, und eine Schnittlinie zwischen der Fase (15, 15A, 15B) und der Nasenradiusfläche (14A) aufweist, die eine Nasenschneidkante (16) bildet, wobei die Nasenschneidkante (16) durch wenigstens einen Radius (R1) definiert ist und die Schneidecke wenigstens eine gekrümmte Planschneide (17, 18) aufweist, wobei der Fasenwinkel (β_C) in einem Querschnitt an der Nasenschneidkante (16) größer ist als der Fasenwinkel in einem Querschnitt in einem Abstand von der Nasenschneidkante (16), dadurch gekennzeichnet, daß die periphere Fase (15, 15A, 15B) in einer Draufsicht eine im wesentlichen konstante Breite (W_A-W_E) hat.

2. Schneideinsatz nach Anspruch 1, dadurch gekennzeichnet, daß der Fasenwinkel (β_C) im Querschnitt an der Nasenschneidkante (16) größer ist als der Fasenwinkel im Querschnitt an der Planschneide.

3. Schneideinsatz nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die periphere Fase als eine Abschrägung (15) vorgesehen ist, die die gesamte Peripherie des Schneideinsatzes umgibt.

4. Schneideinsatz nach einem der vorangegangenen Ansprüche, dadurch gekennzeichnet, daß die periphere Fase (15, 15A, 15B) einer im wesentlichen geraden Linie im Querschnitt durch den Schneideinsatz folgt.

5. Schneideinsatz nach einem der vorangegangenen Ansprüche, dadurch gekennzeichnet, daß die periphere Fase (15, 15A, 15B) an dem Eckenabschnitt (14) einen kontinuierlich variierenden Fasenwinkel (β) hat.

6. Schneideinsatz nach Anspruch 5, dadurch gekennzeichnet, daß der Fasenwinkel (β_C) in einem Querschnitt an der Nasenschneidkante (16) größer ist als der Fasenwinkel (β_E) in einem Querschnitt an einer ersten Planschneide (17, 18).

7. Schneideinsatz nach einem der vorangegangenen Ansprüche, dadurch gekennzeichnet, daß die Schneidecke (14) eine erste Planschneide aufweist, die durch wenigstens einen Radius (R2) definiert ist, und eine zweite Planschneide aufweist, die durch wenigstens einen Radius (R3) definiert ist, wobei die Radien (R1-R3) verschiedene Ursprungspunkte haben.

8. Schneideinsatz nach Anspruch 7, dadurch gekennzeichnet, daß die erste und die zweite Planschneide (17, 18) jeweils einen kontinuierlich variierenden Fasenwinkel (β) haben.

9. Schneideinsatz nach einem der vorangegangenen Ansprüche, dadurch gekennzeichnet, daß der Schneideinsatz (10) teilweise oder vollständig aus kubischem Bornitrid besteht.

Revendications

1. Insert de coupe pour tournage, comprenant une surface supérieure 11), une surface inférieure (12) sensiblement parallèle à ladite surface supérieure, et au moins trois surfaces latérales (13A, 13B) s'étendant entre lesdites surfaces supérieure et inférieure, une transition, entre deux surfaces latérales (13A, 13B) adjacentes, formant une surface à rayon de nez (14A) arrondie à un angle d'insert de coupe (14), ledit insert de coupe comprenant une zone (15, 15A, 15B) périphérique reliant les surfaces supérieure et latérales, au moins à la partie d'angle (14), à un angle de chanfrein (β_A-β_E), et une intersection de ladite zone (15, 15A, 15B) et de ladite surface à rayon de nez (14A) formant un bord de coupe de nez (16), ledit bord de coupe de nez (16) étant défini par au moins un rayon (R1), ledit angle de coupe comprenant au moins un bord racleur (17, 18) incurvé, dans lequel l'angle de chanfrein (β_C) en coupe transversale au bord de coupe de nez (16) est supérieur à l'angle de chanfrein, observé en coupe transversale à une distance du bord de coupe de nez (16), et caractérisé en ce que la zone (15, 15A, 15B) périphérique en vue en plan a une largeur (W_A-W_E) sensiblement constante.

2. Insert de coupe selon la revendication 1, caractérisé en ce que l'angle de chanfrein (β_C) en coupe transversale au bord de coupe de nez (16) est supérieur à l'angle de chanfrein en coupe transversale audit bord racleur.

3. Insert de coupe selon la revendication 1 ou 2, caractérisé en ce que la zone périphérique est prévue sous forme de chanfrein (15) encerclant la totalité de la périphérie de l'insert de coupe.

4. Insert de coupe selon l'une quelconque des revendications précédentes, caractérisé en ce que la zone (15, 15A, 15B) périphérique suit une ligne sensiblement rectiligne en coupe transversale à travers l'insert de coupe.

5. Insert de coupe selon l'une quelconque des revendications précédentes, caractérisé en ce que la zone (15, 15A, 15B) périphérique a un angle de chanfrein (β) variant de manière continue à la partie d'angle (14).

6. Insert de coupe selon la revendication 5, caractérisé en ce que l'angle de chanfrein (β_C) en coupe transversale au bord de coupe de nez (16) est supérieur à l'angle de chanfrein (β_E) en coupe transversale à un premier bord racleur (17, 18).

7. Insert de coupe selon l'une quelconque des revendications précédentes, caractérisé en ce que la partie d'angle (14) comprend un premier bord racleur, étant défini par au moins un rayon (R2), et un deuxième bord racleur, étant défini par au moins un rayon (R3), lesdits rayons (R1 - R3) ayant des points d'origine différents.

8. Insert de coupe selon la revendication 7, caractérisé en ce que chaque premier et deuxième bord racleur (17, 18) a un angle de chanfrein (β)variant de manière continue.

9. Insert de coupe selon l'une quelconque des revendications précédentes, caractérisé en ce que l'insert de coupe (10) est composé, partiellement ou complètement, de nitrure de bore cubique.

Drawing